Braiding machines may be used for a variety of different purposes such as producing ropes or forming a woven coverage around a substrate. For the latter, the coverage is formed by interweaving individual yarns and forming them into a structure around the substrate. The yarns and the substrate itself can take many different forms depending upon the application and the woven coverage that is formed can serve a number of different purposes from reinforcing the underlying substrate to providing a protective layer, providing a separating layer and so on.
A typical braiding machine 1 might be composed of sets of bobbins, typically two, which are arranged to travel along two separate paths. The bobbins have the yarn wound onto them initially so that it can be unwound from the bobbin as it travels along its path. The two paths 11, 12 are arranged (see the solid 11 and dotted 12 lines in FIG. 1) so that as each bobbin 23 travels along its path, it passes between the bobbins travelling on the other path in a generally opposite direction. In this way, half the bobbins travel generally clockwise around the machine whilst the other half travel generally counter-clockwise.
As each bobbin travels along the path it will sequentially pass another bobbin on the other path to the right and then to the left and so on. This in and out movement is transferred to the yarns which extend from the bobbins, as shown in FIG. 2. This in and out motion on the yarns, weaves the yarns into cylindrical sheath around the substrate or work product to be wrapped.
FIG. 2 shows a schematic arrangement of the elements in a braiding process for applying a braid to a substrate 21. The substrate is provided on a reel 20 which pays out the substrate 21 to be fed to a braiding machine 22. The braiding machine 22 includes a number of bobbins 23 mounted on a platform to allow the bobbins to travel along their designated paths. Although in this example, the braiding machine is mounted with a horizontal axis, these machines may be used with a vertical axis as well.
Each bobbin includes a length of yarn which in use is unwound from the bobbin and extends to meet the substrate 21 at the braiding point 25. A number of yarns 24 each extend from one of the bobbins 23 and are wound at the braiding point 25 to form a braided substrate 26. The substrate and the braided substrate are drawn through the braiding machine 22 by a drive or caterpillar 27 which controls the speed at which the substrate passes through the braiding machine. The finished braided substrate is then received onto a storage reel 28.
FIG. 1 shows an example of a braiding machine end on. The circles 23 represent the bobbins travelling along the two paths 11 and 12. The arrows show the direction of travel of the bobbins on each of the paths. In this example, eight bobbins travel along each of the two paths. The bobbins typically include a peg at their bases which travels within the track defining the paths 11, 12 and is driven by a gearing mechanism behind the track plate. The gears are arranged so as to drive the bobbins along their designated tracks and retain them in a suitably spaced arrangement so that the bobbins travel freely around their tracks without interfering with each other.
FIG. 3 shows a more details view of a typical braiding machine. Again, as with the example in FIG. 1, this machine has eight bobbins arranged in each of the two paths giving a total of sixteen bobbins, each feeding a yarn 24 to the braiding point 25. The substrate 21 is typically fed from one side of the machine through the centre of the braiding plate towards the braiding point 25 which lies along the central axis of the machine.
In order to ensure that the braid is uniformly formed and the braids are suitably tightly arranged, the yarns are fed from the bobbin under tension. The bobbin would typically include a tensioning arrangement to provide this tension. It is important that the tension on each of the bobbins is uniform and that the tension in all the bobbins is largely the same. In FIG. 4 it can be seen that the tension on each of the yarns are applied to the substrate at the braiding point 25. Thus the bobbins are generally uniformly arranged around the centre of the braiding point and because the bobbins maintain a consistent tension in each of the yarns, the forces provided by the yarns balances out so that there is no net force on the substrate at the braiding point 25. This ensures that the substrate and the braided product 26 maintain a central position between all the yarns to give a good quality braid product.
Typically each individual bobbin has a pay off station with a mechanical clutch which controls the let off tension of the yarn or wire. The tensions are set prior to starting manufacture. As indicated above, it is important that each bobbin pay off tension is maintained during a production run. If the tensions vary during a production run, this can have a negative effect on the product being manufactured, i.e. the product does not conform to specification which can lead to product not meeting the test criteria, therefore it will not be fit for purpose and will have to be remade.
Under normal operating conditions, with adequate tensions maintained on all the yarns, the braiding process will be completed without problems. However if there is a mechanical failure with one of the bobbins or the yarn payoff mechanism or if a yarn becomes entangled or snagged on some other part of the machine or if one of the yarns breaks or runs out then the normal tensioning arrangement of the machine will be disturbed.
Usually, the main clutch component is a spring assembly. These springs have a tendency to fail periodically without any signs prior to the failure. If a spring snaps during a production run this causes the yarn to pull tight against the substrate (product being manufactured) causing irreparable damage, where the product has to be remade.
FIG. 4 shows schematically what happens if one of the yarns is broken but the effect is similar if the yarn tension is too high or too low. The failure of a yarn will remove the small portion of the tension that is provided by that yarn. This will result in an imbalance in the load applied to the substrate at the braiding point 25. As shown in FIG. 4, the tension provided by the broken yarn will leave a net force on the substrate and will tend to pull it away from its normal position. This displacement of the substrate generally creates a disturbance in the equilibrium of the braiding process and may affect the tensioning of the other yarns which may further exacerbate the problem and cause the substrate to be further deviated from its normal position. This typically results in further failures and damage to the substrate itself.
Again if the clutch mechanism fails either reducing the tension in a yarn or increasing the tension a similar imbalance will occur. Other failure modes are possible such as snagging of the yarn on the clutch mechanism.
The braiding machines themselves typically operate at very high speeds so that if a yarn does break, the effect and the consequences of it can result in the substrate being damaged very quickly long before an operator can stop the machine to rectify the problem. Braiding machines generally do not have very good fail safe mechanisms in place to monitor the product being manufactured, but they normally do stop after a catastrophic failure.
This failure will normally result in the damaged substrate and the previously produced braided product having to be discarded and the entire production process restarted with a new substrate.
The present invention aims to overcome or at least ameliorate some of the problems of the existing braiding machines.